Resolving WpGraphQL query returns null in Next.js

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Understanding the Problem

In this particular scenario, you’re trying to make a GraphQL query to retrieve posts filtered by category slug. However, the response you’re receiving is null, and when attempting to handle the data in getStaticProps, you face serialization errors.

The key code elements producing the errors include:

Your GraphQL query where $slug is defined as a String

Example Code Snippet

Here is the query you initially used, which is attempting to filter by category slug:

[[See Video to Reveal this Text or Code Snippet]]

The Error You Encountered

When directly passing category_IDD as props, you received an error indicating that undefined cannot be serialized.

Using JSON.parse was leading to null responses instead of the expected data.

The Solution: Fixing the Query

Upon investigation, the issue stems from the fact that the GraphQL variable $slug should actually be defined as an array of strings instead of a single string. This is a common requirement when you want to pass multiple slugs or filter multiple categories.

Steps to Resolve the Issue

Update the GraphQL Variable Definition

Change the definition of the $slug variable in your query from:

[[See Video to Reveal this Text or Code Snippet]]

To:

[[See Video to Reveal this Text or Code Snippet]]

The corrected query snippet should look like this:

[[See Video to Reveal this Text or Code Snippet]]

Adjust the Data Handling in getStaticProps

After making this change to the GraphQL query, ensure that your data handling and serialization in getStaticProps properly reflects the data structure returned from the query:

[[See Video to Reveal this Text or Code Snippet]]

Test Your Query

After making the adjustments, run your application and verify that your query now returns the expected data. You should no longer see null responses, and the serialization error should also be resolved!

Conclusion

Working with GraphQL in a headless WordPress setup can come with its challenges, especially when it comes to properly formatting queries and handling returned data. By correcting the $slug variable from a single string to an array of strings, you can successfully resolve the null response issue without facing serialization errors.

Don’t hesitate to test different queries and configurations to find what best works for your project. Happy coding!